System and Method for Enabling Fused Deposition Metal 3D Printing

ABSTRACT

A metal fused, deposition printer, that uses the thixotropic (or other) properties of a metal (or alloy) to control the viscosity of the material being deposited. In the invention presented in this patent, the viscosity of the metal is controlled by shearing it before, during, or after the deposition process. Since thixotropic (or other) properties allow for the control of the viscosity separately from the temperature, the taught invention allows for precise control of the temperature differential between the layer being deposited, and the substrate layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Patent Application Ser. No.62/475,567, entitled “System and Method for Enabling Fused DepositionMetal 3D Printing”, filed on Mar. 23, 2017. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed,and the aforementioned application is hereby incorporated herein byreference.

FEDERALLY SPONSORED RESEARCH

Not Applicable

SEQUENCE LISTING OR PROGRAM

Not Applicable

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to rapid prototyping using 3Dprinters. More specifically, the present invention relates to rapidprototyping using 3D printers where a fused deposition 3D printer takesadvantage on the advancement in polymer based additive manufacturingtechniques.

BACKGROUND OF THE INVENTION

Polymer based fused deposition printers have undergone a decade oftechnical improvements and printers are currently inexpensive andreliable. This transformation is still to be accomplished in the metal3D printing arena. The technologies available have downfalls includingprint size, print time, quality of resulting parts, and overall process.

Many parts being printed today have to undergo an annealing process thatis it not naturally conducive to specific military requirements. Theadvantage of the approach of the present invention is that it is moreamenable to creating systems that are low cost and that bypass many ofthe current challenges: toxic powders, heat treatments, or annealing.

Polymer based fused deposition printers have undergone a decade oftechnical improvements and printers are currently inexpensive andreliable. This same transformation is still to be accomplished in themetal 3D printing arena. The few technologies available have severaldownfalls including print size, print time, quality of the resultingparts, and overall process. For example, many parts being printed todayhave to undergo an annealing process that takes time, and it is notnaturally conducive to Department of Defense (DoD). Also, the rawmaterials used often include very fine metallic powders that are verytoxic or can become explosive under some circumstances.

Although the process of metal 3D printing is currently somewhatcumbersome, being able to print metallic parts in-situ will providesignificant advantages from a logistics standpoint and therefore affectmaintainability and on-time readiness in a way that could berevolutionary to the DoD.

SUMMARY OF THE INVENTION

As mentioned in the topic, there are some technologies like powder bedsthat could be somewhat improved to make the process more appealing tothe DoD requirements. There are significant efforts currently underwaywith the Oak Ridge National Labs and Kansas City Plant that are alreadyaddressing these incremental improvements.

The present invention is a revolutionary new process that uses thethixotropic properties of some metals and alloys to create a fuseddeposition 3D printer that takes advantage on the advancement in polymerbased additive manufacturing techniques. The advantage of the proposedapproach is that is it more amenable to creating systems that are lowcost, easier to deploy, and bypass many of the current challenges: toxicpowders, need for heat treatments, or annealing.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIG. 1 is a flow chart of the method taught by the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the invention of exemplaryembodiments of the invention, reference is made to the accompanyingdrawings (where like numbers represent like elements), which form a parthereof, and in which is shown by way of illustration specific exemplaryembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention, but other embodiments may be utilized andlogical, mechanical, electrical, and other changes may be made withoutdeparting from the scope of the present invention. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined only by the appendedclaims.

In the following description, numerous specific details are set forth toprovide a thorough understanding of the invention. However, it isunderstood that the invention may be practiced without these specificdetails. In other instances, well-known structures and techniques knownto one of ordinary skill in the art have not been shown in detail inorder not to obscure the invention. Referring to the figures, it ispossible to see the various major elements constituting the apparatus ofthe present invention.

The present invention is a revolutionary new process that uses thethixotropic properties of some metals and alloys to create a fuseddeposition 3D printer that takes advantage on the advancement in polymerbased additive manufacturing techniques. The advantage of the proposedapproach is that is it more amenable to creating systems that are lowcost, easier to deploy, and bypass many of the current challenges: toxicpowders, need for heat treatments, or annealing

Thixotropy is a time-dependent shear thinning material propertyexhibited by some metals and alloys. Under certain conditions thesemetals are thick (viscous) but will flow (become thin, less viscous)over time when shaken, agitated, sheared or otherwise stressed even ifthe temperature is not increased. In other words, thixotropic materialscan change viscosity either by changing their temperature or byshaking/shearing them. This is very advantageous because it can allowfor the independently control (from viscosity) of the temperature andheat transfer characteristics between the newly deposited layer and theprevious layer in a 3D printer. Not all metals are thixotropic in theirraw state; for example, aluminum transforms from solid to liquid havingonly a very small area where it exhibits these properties.

Viscosity is a core characteristic utilized by fused deposition 3Dprinters. As the polymer exits the tip, it is hot and it easily flowsout of the tip, but its viscosity quickly changes as it adheres to theprevious layer. The heat transfer is controlled using the substrate andchamber temperature to provide a good bonding/fusion between layers. Thesame viscous properties are important in many manufacturing processes.

For example, although Aluminum alloys are often die casted, they areseldom injection molded. One of the reasons is that as the moltenaluminum is injected, it is either solidifies too quickly and causesvoids in the part or runs too fast creating bubbles as it cools.Maintaining a constant speed and propagation of the material in the moldbecomes significantly more cumbersome with materials that do not exhibitsome level of viscosity.

In the past few years, the thyrotrophic properties of some alloys havebeen exploited to improve the metal injection molding process (dubbedThixomolding because of the thixotropic properties). It is likely thatthe reviewer of this application has a smart phone in his/her pocketwhose case was built using Magnesium Thixomolding.

One more important property is that metals that have significantThixotropic areas do not often create internal stresses that need to beheat treated or annealed, saving a slow, costly, and energy intensivestep in the manufacturing process.

The same thixotropic properties that have revolutionized metal injectionmolding can be used to create a metal fused deposition 3D printer thatuses the Thixotropic zone to overcome many of previous attempts at thetechnology.

Magnesium alloy AZ91D is a good candidate because it is the alloy mostcommonly used for thixomolding. For example, the Samsung Galaxy 7 phonescasing is built using a Magnesium alloy. These alloys are lighter thanaluminum with very similar mechanical properties. The corrosion andoxidation characteristics are also similar to aluminum from a durabilitystandpoint. These alloys also provide significant RF/EMI shielding andbetter than aluminum heat conductivity.

The proposed fused deposition 3D printer system 100 will be composed offour main components: a liquefier 101, extrusion nozzle 102, a chamber103, and an x, y, z table 104.

The liquefier will include the heating elements, and a device forshearing (mixing) the semi-molten metal 105.

The liquefier will control temperature and the viscosity of the materialshearing and therefore bringing the slurry to a thixo state 109. Theliquefier will add material by either driving a wire with the rawmaterial or a screw (ala injection molding). The means of adding newmaterial will also be used for controlling the speed of the materialbeing deposited 110.

The extrusion nozzle will be made out of an iron rich alloy (currentlyused in some polymer printers). Magnesium is strongly repelled by iron,providing for cleaner process 108.

The xyz table will be designed to accommodate the print size requestedin the topic 106. Because AZ91D has very little shrinkage, the inventorsexpect that large prints will be possible without the usualcomplications associated with metal printing and shrinkage.

Finally, the chamber will house the system and maintain temperatures toallow for fusion between the layers 107. Although AZ91D oxidizes, it isless prone to fast oxidation like AL, therefore, the inventors expectthat the inventors will get away without having have a fully air tightchamber as required by other processes, however, some inert gas may benecessary to delay surface oxidation and for good bonding.

Metal fused deposition is the holy grail of metal 3D printing, theinventors are proposing in this research to extend the advances made inThixomolding into the 3D printing arena. The inventors are alreadybuilding 3D printers to provide sterile polymer printing to warfighters,and therefore uniquely placed to do this research.

The major tasks include: designing a liquefier that can melt the alloyand control the thixo properties of the slurry to create the sufficientamount of viscosity to allow flow and provide good bonding. The x, y, zand nozzles table can be leveraged from other ongoing programs, and thechamber will need to be designed to meet the temperature and gasrequirements.

The benefits could be revolutionary. The inventors are proposing a lowcost, low energy requirements metal printer that can be deployed, andmore importantly can print parts in single steps that need little postprocessing.

Thixomolding is currently used as a manufacturing process for manydevices including airplane, and automotive markets. Polymer depositionis commercially available and low cost. The combination of the twotechnologies has not been previously researched.

The inventors see two main risks: stable repeatable bonds between layersand surface oxidation during printing process. As explained earlier,being able to control the thixo properties of the slurry will allow usto change the temperatures of the substrate and the bead, and therefore,controlling the heat transfer and temperature of the bond becomeseasier. Surface oxidation can be solved by closing the chambers.

Although the present invention has been described in considerable detailwith reference to certain preferred versions thereof, other versions arepossible. Therefore, the point and scope of the appended claims shouldnot be limited to the description of the preferred versions containedherein.

As to a further discussion of the manner of usage and operation of thepresent invention, the same should be apparent from the abovedescription. Accordingly, no further discussion relating to the mannerof usage and operation will be provided.

With respect to the above description, it is to be realized that theoptimum dimensional relationships for the parts of the invention, toinclude variations in size, materials, shape, form, function and mannerof operation, assembly and use, are deemed readily apparent and obviousto one skilled in the art, and all equivalent relationships to thoseillustrated in the drawings and described in the specification areintended to be encompassed by the present invention.

Therefore, the foregoing is considered as illustrative only of theprinciples of the invention. Further, since numerous modifications andchanges will readily occur to those skilled in the art, it is notdesired to limit the invention to the exact construction and operationshown and described, and accordingly, all suitable modifications andequivalents may be resorted to, falling within the scope of theinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method for 3D printingmetal, comprising the steps of: a liquefier for melting or semi-meltingthe metal into a slurry; a shearing mechanism used to vary the viscosityof the slurry within the thixotropic range; a nozzle, extender, orsprayer to dispense the slurry onto the substrate; and a mechanism formoving the nozzle or extender as the slurry is deposited, or a mechanismfor moving the part as the slurry is being deposited.
 2. The method inclaim 1, further comprising the step of enclosing the mechanism into achamber.
 3. The method in claim 1, further comprising the step ofcontrolling the temperature of the chamber, or directly controlling thesurface temperature of the part (laser or otherwise).
 4. The method inclaim 1, further comprising the step of shaking the deposited part, inorder to control the viscosity of the deposited layer.
 5. The method inclaim 1, wherein the liquefier uses a screw to feed the material (chipsor powder) into the heating chamber, and to maintain the desiredpressure at the nozzle or extender.
 6. The method in claim 1, whereinthe liquefier controls the pressure of the material inside of theheating chamber by controlling the speed of the feed wire.
 7. The methodin claim 1, wherein the metal being used is doped with other materials,which enhance or modify the thixotropic region (metals such asattapulgite, etc.).
 8. The method in claim 1, wherein the shearing ofthe material (to control viscosity) occurs before it exits the nozzle orextruder, and is performed by a mixing stage; in this stage, the metalis sheared by rotating arms, or by forcing the metal through tightopenings.
 9. The method in claim 1, wherein the shearing of the material(to control viscosity) occurs before it exits the nozzle or extruder, byshaking the metal inside of the liquefier, or in a stage directly beforethe nozzle or extruder.
 10. The method in claim 1, wherein the shearingof the material (to control viscosity) occurs at the nozzle or extruder,and the size of the extruder's opening can be dynamically controlled, orby manually changing the nozzle or extruder.
 11. The method in claim 1,wherein the temperature of the substrate part and the extruded metal isoptimally maintained to enhance fusion, while the viscosity of theextruded metal is controlled independently by shearing the metal into adifferent thixotropic region.
 12. The method in claim 1, wherein theextruded material can be deposited into a chamber, within a range oftemperatures, and still maintain the viscosity compatible with the fuseddeposition process.
 13. The method in claim 1, wherein rheopecticproperties are used to increase the viscosity of the substrate, toimprove fusion.
 14. A system for computing the doping amount necessaryto enhance the thixotropic or rheopectic properties of the metal toachieve viscosities and temperatures suitable for 3D printing.
 15. A 3Dprinter, where the extruded material is the same temperature as thesubstrate, but the viscosity of the extruded material is controlledthrough shearing.
 16. A 3D printer, where the same shrinking propertiesas the extruded material are shared by the area onto which the part isprinted.